1. Field of the Invention
The present invention relates generally to a conveyor system for transporting flatbed trucks, skids or the like (hereinafter occasionally referred to as "load-support members") through a yard or a plant with or without a load being carried on each load-support member. More particularly, the present invention relates to a conveyor system including driven and driven carriers on which the load-support members are supported.
2. Description of the Related Art
Various types of conveyors are used for transporting load-support members, such as flatbed trucks or skids, through a yard or a plant.
In an automated vehicle assembly line, works such as vehicle bodies are painted, then transferred into a drying oven for drying the coated paint while they are carried on flatbed carriages or trucks. FIGS. 11 and 12 exemplify a conventional flatbed truck used for transporting the painted vehicle bodies through the drying oven. The conventional truck A1 has four flanged wheels A2 (two being shown) rotatably mounted to the underside of a body of the truck A1. The wheels A4 are carried on a pair of guide rails A4 fixed to a support frame or base A3 placed on a floor surface A of the drying oven. The truck A1 travels along the guide rails A4 as it is pulled or dragged by a truck conveyor A5 located centrally between the guide rails A4.
When the truck A is advanced along a curved path, the wheels A2 fail to smoothly move through a curved portion of the guide rails A4 due to a relatively small radius of curvature of the curved path. To cope with this problem, the conventional flatbed truck further has four casters A6 mounted on the underside of the truck body interiorly of the wheels A2. The casters A6 thus provided act for the wheels A2 in supporting truck A1.
As shown in FIG. 12, the curved path is devoid of the guide rails A4 (FIG. 11) on which the wheels A2 are supported, but it includes a pair of laterally spaced guide tracks A7 attached to a support frame A8 for supporting thereon the casters A6.
The truck conveyor A5 has a succession of trolleys A11 (only one being shown) each supported by two pair of guide rollers A10 received in a pair of confronting channel-shaped guide rails A9 for rolling movement along the guide rails A9.
The trolley A11 is connected to a conveyor chain A12 so as to suspend the conveyor chain A12, as shown in FIG. 13. The trolley A11 supports a pusher dog A13 and a retainer dog A14 above the guide rails A9 so that these dogs A13, A14 are pivotally movable about pivot pins A15, A16, respectively.
A tow pin A17 provided on the underside of the body of the truck A1 is inserted between the pusher dog A13 and the retainer dog A14. When the conveyor chain A12 is driven, the pusher dog A13 pushes the tow pin A17 forward to thereby advance the truck A1.
FIG. 14 shows a conventional roller conveyor for transporting works via skids. The roller conveyor B1 includes a number of support frame or base B2 installed on a floor surface along a conveyance path, a series of flanged free or idle rollers B3 arranged along the conveyance path and each supported on one end of each support frame B2, and a series of drive rollers B4 arranged along the conveyance path and each supported on the other end of each support frame B2 in confronting relation to the corresponding flanged idle roller B3.
Each of the flanged idle rollers B3 is freely rotatable about a horizontal axis and supports thereon the undersurface of a roller engagement portion t of one leg B6 of the skid B5 while opposite sides of the roller engagement portion t are guided between opposite annular flanges F, F of the flanged idle roller B3.
Each of the drive rollers B4 carries thereon the undersurface of the other leg B6 of the skid B5. Upon rotation of the drive rollers B4, the skids B5 is conveyed along the conveyance path.
In the conventional conveyor system shown in FIGS. 11-13, because the wheels A2 are fixed in orientation relative to the tuck body, the flatbed truck A1 can travel along the guide rails A4 extending along a straight-line conveyance path or a gently curved conveyance path. For enabling the flatbed truck A1 to travel along a curved conveyance path with small radius of curvature, the casters A6 designed to roll along the caster tracks A7 must be used in place of the wheels A2.
Thus, the flatbed truck A1 is rendered complicated in construction and increases the equipment cost due to the necessity of the guide rails A and the caster tracks A7.
In the roller conveyor B1 shown in FIG. 14, one leg B6 of the skid B5, which in general is made relatively long in the conveyance direction, is guided between the respective annular flanges F of the idle rollers B3. Accordingly, at a curved portion of the conveyance, smooth conveyance of the skid B5 is difficult to achieve. To cope with this problem, a turntable is used to change the direction of the skid. However, use of the turntable may pose a limitation about the layout design of conveyance path.
According to another conventional attempt, a trolley conveyor is employed in which a skid is conveyed while being carried on carriages. However, the trolley conveyor requires a large vertical conveyance space. Additionally, since the carriages have substantially the same area as the skids, the carriages occupy a large area even when they move along a return path with no loads carried thereon.
Furthermore, conventional slat conveyors used for conveyance of the flatbed trucks or the skids are not successful because in order to transport the tracks or the skids along a curved path, a turntable must be used to change the direction of the tracks or the skids.
Additionally, since the conveyors disposed in different processing stations each have a particular design well suited for a process achieved in the corresponding station, the conventional conveyor systems are unable to handle different types of load-support members, such as trucks and skids, without reconstruction of conveyors.